Fluid cylinder assembly

ABSTRACT

A fluid cylinder assembly of the kind provided with a cylinder tube in which a piston coupled by a piston rod operates. The cylinder tube has one end connected with a rod cover. The piston rod passes through an aperture in the rod cover and projects outwardly. The rod cover is associated with means for mounting the fluid cylinder assembly on a frame and a load transducer which converts a change in load axially acting thereon to a change in voltage or current and develops an electric signal. The movement of a lead wire extending outwardly of the load transducer is precluded, and the results of measurement are obtained with a high degree of accuracy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a fluid cylinder assembly incorporating loadtransducers (as defined hereinafter) for detecting the thrust exerted bya piston rod.

2. Description of the Prior Art

The prior art fluid cylinder assembly is useful for various purposessuch as subjecting a component part of a machine to press fit, clamping,chucking, roller pressure or stamping. According to the purpose forwhich the fluid cylinder assembly is used, it is necessary to detect themagnitude of thrust exerted by a piston rod or the magnitude of loadacting on the component part.

For example, when a component part of a machine is subjected to pressfit, force exerted thereon is measured with a view to using the measuredvalue for passing a judgment on whether or not the component part hasbeen properly subjected to press fit.

It is known to measure such force by means of a load cell carried eitheron the outer end of the piston rod (as disclosed in Japanese UtilityModel Registration No. 2,569,871) or on a cap cover secured on the endof a cylinder tube opposite the end at which the piston rod isextendible and retractable.

The load cell carried on the outer end of the piston rod assures thatthe results of measurement are obtained with a high degree of accuracy,because the magnitude of load acting on the component part can bedirectly measured. The trouble is that a lead wire extending outwardlyof the load cell moves as the piston rod moves. Therefore, a supportingmember or members have to be employed as a means to movably support thelead wire and prevent it from being disconnected.

In case of the load cell carried on the cap cover, the output taken fromthe load cell contains not only the magnitude of load acting on thecomponent part but also the magnitude of gravity acting on the fluidcylinder assembly per se. Especially when the fluid cylinder assembly ismounted on a vertical supporting structure in cantilever fashion, i.e.,with the cap cover allowed to support the gross weight of the fluidcylinder assembly, the output taken from the load cell contains not onlythe magnitude of thrust acting on the component part but also themagnitude of angular moment acting on the fluid cylinder assembly perse. A marked decline in the accuracy of measurement results therefrom.

SUMMARY OF THE INVENTION

The present invention is concerned with eliminating the aforesaiddifficulty. As such, the primary object of the invention is to provide afluid cylinder assembly which precludes the movement of a lead wireextending outwardly of a load cell and allows the results of measurementto be obtained with a high degree of accuracy.

As indicated above, the invention is concerned with a fluid cylinderassembly of the kind provided with a cylinder tube 11 in which a piston12 coupled by a piston rod 13 operates. The cylinder tube 11 has one endconnected with a rod cover 14. The piston rod 13 passes through anaperture in the rod cover 14 and projects outwardly. In one describedembodiment, the rod cover 14 is associated with means 27 for mountingthe fluid cylinder assembly on a frame FM and a transducer whichconverts a magnitude in load axially acting thereon to a magnitude involtage or current and develops an electric signal (hereinafter referredto as the “load transducer”).

In another described embodiment, the load transducer includes twoflanges lying on, and perpendicular to, the axis of the fluid cylinderassembly and disposed in spaced parallel relation with each other. Athin cylindrical wall capable of elastic deformation is interposedbetween, and integrally formed with, these two flanges and extendscoaxially of the fluid cylinder assembly. At least one strain sensor ismounted on the thin cylindrical wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary front view of one embodiment of the invention;

FIG. 2 is a bottom plan view thereof;

FIG. 3 is a sectional view of a part thereof where a strain gauge ismounted;

FIG. 4 is a front view of another embodiment of the invention;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is a sectional view of a plate-shaped member;

FIG. 7 provides a circuit diagram of an example of an electrical circuitincorporated in the strain gauge; and

FIG. 8 provides a circuit diagram of an example of how to make aconnection for the strain gauges.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

In FIGS. 1 and 2, the numeral 1 designates a fluid cylinder assembly ofa first embodiment. FIG. 3 is a sectional view of a part of a loadtransducer 23 incorporated therein where a strain gauge GU1 is mounted.

The fluid cylinder assembly 1 shown in FIGS. 1 and 2 comprises acylinder tube 11, piston 12, piston rod 13, rod cover 14, cap cover 15,four tie bolts 16 a to 16 d, gland ring 22, load transducer 23, flange24 and bush 25.

The load transducer 23 is made up of flanges 41 and 42, thin cylindricalwall 43 and strain gauges GU1, GU2, etc. The flange 41 serves to connectthe load transducer 23 with the rod cover 14 by means of tie bolts 16 ato 16 d threaded into holes 41 a to 41 d in the flange 41. The flange 24is connected with the flange 42 of the load transducer 23 by means ofbolts 26 a to 26 d threaded into holes 42 a to 42 d in the flange 42through the flange 24. The outer surface of the thin cylindrical wall 43curves towards the top and the bottom and terminates with a largercompass than the middle portion so as to form the flanges 41 and 42. Thethin cylindrical wall 43 undergoes elastic deformation in proportion tothe magnitude of thrust acting thereon.

Referring now to FIGS. 1 to 3, four strain gauges GU1 to GU4 are adheredto four circumferentially equidistantly spaced positions respectively onthe outer surface of the thin cylindrical wall 43 so as to be strainedin response to load axially acting on the region between the flanges 41and 42 and generate a signal proportional to the load. A lead wireextending outwardly of each strain gauge GU is connected to anamplifier.

The piston 12 is slidably mounted in the bore of the cylinder tube 11.The piston rod 13 coupled by the piston 12 moves together with thepiston 12. The piston rod 13 passes through an aperture in the rod cover14 and projects outwardly.

The rod cover 14, cap cover 15, cylinder tube 11 and load transducer 23are associated with each other as follows: The holes 41 a to 41 d in theflange 41 are tapped to engage the threaded ends of the tie bolts 16 ato 16 d respectively. Each of the tie bolts 16 a to 16 d has the otherthreaded end passing through an aperture in the cap cover 15 and thenallowing a nut to be threaded tightly thereupon.

As has been above explained, the flange 24 is connected with the flange42 of the load transducer 23 by means of bolts 26 a to 26 d threadedinto holes 42 a to 42 d in the flange 42 through the flange 24. Theflange 24 is provided with holes 27 to be engaged by bolts (not shown)for mounting the fluid cylinder assembly 1 on the frame FM.

A fluid under pressure can be introduced into the interior of thecylinder tube 11 through ports (not shown) provided in the rod cover 14and the cap cover 15 to cause the piston rod 13 to assume the retractedand extended positions respectively.

The space between the piston rod 13 and the internal surface of the loadtransducer 23 is sufficient to permit the enclosure of grease. Thepiston rod 13 may possibly lightly abut against the internal surface ofthe bush 25. Such abutment has been found undesirable in order to obtainthe results of measurement with a high degree of accuracy. A seal 31,which serves also as a seal, is provided on the internal surface of thegland ring 22. A scraper 32 is provided on the internal surface of thebush 25. The provision of the scraper 32 has also been found undesirablein order to obtain the results of measurement with a high degree ofaccuracy.

The application of the fluid cylinder assembly 1 to a case where a fluidunder pressure is introduced into the interior of the cylinder tube 11through a port provided in the cap cover 15 to cause the piston rod 13to assume an extended position so as to allow the outer end of thepiston rod 13 to subject a component part of a machine to press fit willnow be described as an example of the manner in which the fluid cylinderassembly 1 works.

When the piston rod 13 is assuming an extended position, the fluidcylinder assembly 1 generates a thrust which is substantially equal tothe force exerted on the component part. This thrust is axially appliedto the load transducer 23 and causes the thin cylindrical wall 43 to bedeformed. Then the strain gauges GU generate signals, which aresubjected to arithmetic operations so that the magnitude of the thrustmay be found.

The output taken from the load transducer 23 contains not only themagnitude of thrust acting on the component part but also the magnitudeof gravity acting on the fluid cylinder assembly per se. However, thisgravity has a known fixed quantity and can be easily corrected bycalculation.

When the load transducer 23 undergoes force other than axial force, e.g.bending moment or torsional moment, the undesirable effect of such forcecan be circumvented by using appropriate strain gauges GU and by makingan appropriate connection therefor.

It will be appreciated that certain significant advantages are obtainedfrom the fluid cylinder assembly 1 as follows: The load transducer 23permits the measurement of thrust to be carried out easily and with ahigh degree of accuracy. Since the load transducer 23 does not moveduring measurement, the movement of lead wires extending outwardly ofthe strain gauges GU is precluded. Therefore, the lead wires can besecured to a supporting structure. A wiring plan can be readily carriedinto effect, and yet the possibility of disconnection is obviated.

Dust and/or oil attached to the piston rod 13 is scraped away by thescraper 32. Thus the surface of the piston rod 13 is substantiallycompletely cleaned such that dust and/or metal powder is prevented fromgetting into the cylinder tube 11. However, the invention is based onthe realization that the scraper 32 does not necessarily need to beused.

The strain gauges GU may be coated with a synthetic resin for theprotection thereof. Alternatively, they may be provided with a cover.

Second Embodiment

In FIGS. 4 and 5, the numeral lb designates a fluid cylinder assembly ofa second embodiment. FIG. 6 is a sectional view of a plate-shaped member51 used therein. Like numerals are employed to designate component partsfunctioning in substantially the same manner as the previously describedones. These component parts will need no further description, or it willbe sufficient to comment briefly thereon.

Referring now to FIGS. 4 and 5, the plate-shaped member 51 is mounted onthe rod cover 14. Four holes 66 a to 66 d are disposed closer to thecenter of the plate-shaped member 51 and are tapped to engage thethreaded ends of the tie bolts 16 a to 16 d respectively, by which thecomponent parts constituting the fluid cylinder assembly 1 b areassociated with each other.

Another four holes 67 are disposed closer to the edges of theplate-shaped member 51. These holes 67 are to be engaged by bolts (notshown) for mounting the fluid cylinder assembly 1 b on the frame FM.

The central region where the holes 66 a to 66 d are disposed and theedge regions where the holes 67 are disposed are maintained in separatedrelationship by slits 61 and 62 opening through the upper and bottomsurfaces (as viewed on FIG. 4) of the plate-shaped member 51. Recesses63 and 64 are provided in one and the other end portions respectively ofeach slit such that each recess lies across both slits 61 and 62. Straingauges GU1 and GU2 are adhered to thin portions 63 a and 64 a formed bythe recesses 63 and 64 respectively.

Each of the recesses 63 and 64 is provided with a hole 69 through whicha lead wire extending outwardly of each strain gauge GU passes.

Force exerted on the central region where the holes 66 a to 66 d aredisposed is bound to act on the thin portions 63 a and 64 a and subjectthem to elastic deformation. Then the strain gauges GU generate signalsproportional to the magnitudes of strain.

Thus the plate-shaped member 51 constitutes a combination of a loadtransducer and means for mounting the fluid cylinder assembly on theframe FM. The thrust generated by the fluid cylinder assembly 1 b ismeasured on the basis of signals generated by the strain gauges GUadhered to the plate-shaped member 51.

Particular advantages obtained from the fluid cylinder assembly 1 breside in the facts that the strain gauges GU adhered to theplate-shaped member 51 permit the measurement of thrust to be carriedout easily and with a high degree of accuracy and that, since theplate-shaped member 51 does not move during measurement, the movement oflead wires extending outwardly of the strain gauges GU is precluded.

Since the strain gauges GU are arranged in the recesses 63 and 64, theyare free from outside interference.

While the second embodiment has been described particularly inconnection with two recesses 63 and 64 provided in one side of theplate-shaped member 51, it will of course be apparent to those skilledin the art that another two recesses may be provided in the other sidethereof so that there may be a total of four strain gauges GU adhered tofour recesses respectively.

FIG. 7 provides a diagrammatic illustration of an example of anelectrical circuit incorporated in the strain gauge GU, and FIG. 8provides a diagrammatic illustration of an example of how to make aconnection for the strain gauges GU1 to GU4.

The strain gauge GU shown in FIG. 7 includes two resistive elements Aand B. An increase or decrease in the resistance of each of these tworesistive elements A and B depends on the direction in which it isexpanded or contracted. When the strain gauge GU as a whole is expandedvertically as viewed on FIG. 7, a decrease in the resistance of theresistive element A and an increase in the resistance of the resistiveelement B occur. Converses occur when the strain gauge GU as a whole iscontracted vertically as viewed on FIG. 7.

Referring now to FIG. 8, four strain gauges GU1 to GU4 are connected toform a bridge. Each of four nodes of this bridge is constituted by apoint TC where the terminals of two resistive elements A and B meet ineach strain gauge GU. The resistive element A of one strain gauge GU isconnected to the resistive element A of another strain gauge GU adjacentthe first mentioned strain gauge GU, and the resistive element B of onestrain gauge GU is connected to the resistive element B of anotherstrain gauge GU adjacent the first mentioned strain gauge GU.

The input to the circuit is applied across the diagonally opposite nodesEA and EB of the circuit such that constant voltage across them is about10 volts, and the output is taken from the remaining two nodes UA andUB. For zero adjustment to correct the imbalance between the straingauges GU, a resistor having the same temperature characteristic as thestrain gauges GU may be connected either across the nodes EA and UB oracross the nodes EA and UA.

The arrangement of resistive elements to be employed when two straingauges GU are used instead of four is such that a pair of opposite armsof the bridge consist of two resistive elements A respectively andanother pair of opposite arms of the bridge consist of two resistiveelements B respectively.

Various types of strain gauges may be used as the strain gauges GU. Aconnector or a terminal block may be used for connecting a lead wireextending outwardly of each strain gauge GU. Nuts may be used forsecuring the flanges 41 and 42 of the load transducer 23 in positionwith respect to the proximate surfaces. Many modifications andvariations are possible with respect to the construction, shape anddimensions of the cylinder tube 11.

Changes in the construction, shape, dimensions and material of the loadtransducer 23, thin cylindrical wall 43, plate-shaped member 51, slits61 and 62, and fluid cylinder assemblies 1 and 1 b may be made withoutdeparting from the nature and principle of the invention.

What is claimed is:
 1. A fluid cylinder assembly provided with acylinder tube in which a piston coupled by a piston rod operates, saidcylinder tube having one end connected with a rod cover, said piston rodpassing through an aperture in said rod cover and projecting outwardly,the improvement comprising: means for mounting the fluid cylinderassembly on a frame of a supporting structure; a load transducer whichconverts a magnitude in load axially acting thereon to a magnitude involtage or current and develops an electric signal accordingly; and saidmeans and said load transducer being associated with said rod cover. 2.A fluid cylinder assembly as defined in claim 1, wherein said loadtransducer comprises: two flanges lying on, and perpendicular to, theaxis of the fluid cylinder assembly and disposed in spaced parallelrelation with each other; a thin cylindrical wall capable of elasticdeformation interposed between, and integrally formed with, said twoflanges and extending coaxially of the fluid cylinder assembly; and atleast one strain sensor mounted on said thin cylindrical wall.
 3. Afluid cylinder assembly as defined in claim 2, wherein said thincylindrical wall includes an inner cavity adapted to enclose greasetherein.
 4. A fluid cylinder assembly as defined in claim 2, whereinsaid piston rod and said load transducer are maintained in spacedrelation.
 5. A fluid cylinder assembly as defined in claim 2, whereinone of said two flanges disposed farther from said cylinder tube isconnected with a flange for mounting the fluid cylinder assembly on saidframe of said supporting structure.
 6. A fluid cylinder assembly asdefined in claim 5, wherein a scraper for cleaning the surface of saidpiston rod is provided on the internal surface of said flange formounting the fluid cylinder assembly on said frame of said supportingstructure.
 7. A fluid cylinder assembly as defined in claim 1, whereinsaid load transducer and said means for mounting the fluid cylinderassembly on a frame of a supporting structure are combined in aplate-shaped member having a central region and edge regions spacedtherefrom by slits opening through an obverse side and a reverse side ofsaid plate-shaped member, said central region serving to connect withsaid rod cover, and said edge regions serving to mount the fluidcylinder assembly on said frame of said supporting structure.
 8. A fluidcylinder assembly as defined in claim 7, wherein said slits aresymmetrically disposed at each side of a line intersecting the axis ofsaid piston rod.
 9. A fluid cylinder assembly as defined in claim 8,wherein the distance between said two slits is decreased in two portionssymmetrical about the axis of said piston rod, said two portions beingadapted to be subjected to elastic deformation.
 10. A fluid cylinderassembly as defined in claim 9, wherein recesses are provided in saidtwo portions respectively.
 11. A fluid cylinder assembly as defined inclaim 10, wherein strain sensors are mounted in said recesses, saidstrain sensors together with said two portions constituting said loadtransducer.